Titanium(IV) Citrate Speciation and Structure under Environmentally and Biologically Relevant Conditions

Abstract

The water-soluble complexes of Ti(IV) with citrate are of interest in environmental, biological, and materials chemistry. The aqueous solution speciation is revealed by spectropotentiometric titration. From pH 3-8, given at least three equivalents of ligand, 3:1 citrate/titanium complexes predominate in solution with successive deprotonation of dangling carboxylates as the pH increases. In this range and under these conditions, hydroxo- or oxo-metal species are not supported by the data. At ligand/metal ratios between 1:1 and 3:1, the data are difficult to fit, and are consistent with the formation of such hydroxo- or oxo- species. Stability constants for observed species are tabulated, featuring log beta-values of 9.18 for the 1:1 complex [Ti(Hcit)](+), and 16.99, 20.41, 16.11, and 4.07 for the 3:1 complexes [Ti(H(2)cit)(3)](2-), [Ti(H(2)cit)(Hcit)(2)](4-), [Ti(Hcit)(2)(cit)](6-), and [Ti(cit)(3)](8-), respectively (citric acid = H(4)cit). Optical spectra for the species are reported. The complexes exhibit similar yet distinct spectra, featuring putative citrate-to-Ti(IV) charge-transfer absorptions (lambda(max) approximately 250-310 nm with epsilon approximately 5000-7000 M(-)(1) cm(-1)). The prevailing 3:1 citrate/titanium ratio in solution is supported by electrospray mass spectrometry data. The X-ray crystal structure of a fully deprotonated tris-citrate complex Na(8)[Ti(C(6)H(4)O(7))(3)].17H(2)O (1) (or Na(8)[Ti(cit)(3)].17H(2)O) that crystallizes from aqueous solution at pH 7-8 is reported. Compound 1 crystallizes in the triclinic space group P, with a = 11.634(2) Angstroms, b = 13.223(3) Angstroms, c = 13.291(3) Angstroms, V = 1982.9(7) Angstroms(3), and Z = 2.

Application of Water-Soluble Titanium Complexes as Precursors for Synthesis of Titanium-Containing Oxides via Aqueous Solution Processes

“…As the pH of the solution is increased, more highly deprotonated citric acid species are coordinated to titanium. Indeed, crystallization of [Ti(H 2 cit*) 3 6 reported stability constants (¢-values) and a species distribution diagram for titanium(IV) citrato complexes in aqueous solutions determined by potentiometric titration. The proposed model that best fit the potentiometric data was composed of the following equilibrium system:…”

“…Another important application of new water-soluble titanium complexes includes their use as counter anions for forming "compound precipitations" containing two metal ions in the ratio required by the stoichiometry of the target oxide material, such as Ba[Ti(C 6 26 By controlling the pH, temperature, and concentration of the reaction solution, citratoperoxotitanate(IV) ion, [Ti(…”

“…First, let us suppose a hypothetical hydrated species of titanium, [Ti(H 2 O) 6 2¹ indicates a greatly reduced interaction between Ti in [Ti(la) 3 ] 2¹ and O in water. As a result, the mean electronegativity changes from » r = 2.85 for the fully hydrated Ti ion to » r = 2.39 for the Ti lactate complex.…”

Bringing Radiotracing to Titanium-Based Antineoplastics: Solid Phase Radiosynthesis, PET and ex Vivo Evaluation of Antitumor Agent [45Ti](salan)Ti(dipic)

“…Despite the promising physical characteristics, 45 Ti radiochemistry is currently underdeveloped due to the hydrolytic instability of Ti(IV) in aqueous environments. While the titanium citrate complex is mildly stable 20 , previous radiochemical application of […”

The effect of simultaneous magnesium application on the biological effects of titanium

“…The following leaf sprays (30 ml per pot) were used: (i) deionized H 2 O; (ii) Mg sulphate solu- Collins et al (2005) that the reaction of TiCl 4 with at least three equivalents of citric acid (in pH range 3-8) produces 3:1 citrate/titanium complexes with successive deprotonation of carboxylates as the pH increases. In this range and under these conditions, hydroxo-or oxo-metal species are believed not to be present in solution; thus 3:1 citrate/titanium complex could be expected as the active form in this experiment.…”